Unicast trunking in a network device

ABSTRACT

A network device for selecting a port from a trunk group to transmit a unicast packet on the selected port. The network device includes at least one trunk group including a plurality of physical ports. The network device also includes a table with a plurality of entries. Each entry is associated with one trunk group and includes a plurality of fields that are associated with ports in the trunk group. Each entry also includes a hash field that is used to select bits from predefined fields of an incoming unicast packet to obtain an index bit for accessing one of the plurality of fields. The network device further includes transmitting means for transmitting the unicast packet to a port associated with an accessed one of the plurality of fields.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. Provisional Patent ApplicationSer. No. 60/631,548, filed on Nov. 30, 2004 and U.S. Provisional PatentApplication Ser. No. 60/686,456, filed on Jun. 2, 2005. The subjectmatter of these earlier filed applications is hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a network device in a data network andmore particularly to a system and method of creating a logical port bylogically linking multiple ports and for transmitting unicast packetsthrough the logical port.

2. Description of the Related Art

A packet switched network may include one or more network devices, suchas a Ethernet switching chip, each of which includes several modulesthat are used to process information that is transmitted through thedevice. Specifically, the device includes an ingress module, a MemoryManagement Unit (MMU) and an egress module. The ingress module includesswitching functionality for determining to which destination port apacket should be directed. The MMU is used for storing packetinformation and performing resource checks. The egress module is usedfor performing packet modification and for transmitting the packet to atleast one appropriate destination port. One of the ports on the devicemay be a CPU port that enables the device to send and receiveinformation to and from external switching/routing control entities orCPUs.

A current network device may support physical ports and logical/trunkports, wherein each trunk port includes a set of physical external portsand the trunk port acts as a single link layer port. Ingress anddestination ports on the device may be physical external ports or trunkports. By logically combining multiple physical ports into a trunk port,the network may provide greater bandwidth for connecting multipledevices. If one port in the trunk fails, information may still be sentbetween connected devices through other active ports of the trunk.Therefore, trunk ports enable the network to provide greater redundancybetween connected network devices.

In order to transmit information from one network device to another, thesending device has to determine if the packet is being transmitted to atrunk destination port. If a destination port is a trunk port, thesending network device must dynamically select a physical external portin the trunk on which to transmit the packet. The dynamic selection mustaccount for load sharing between ports in a trunk so that outgoingpackets are adequately distributed across the trunk.

Typically, each packet entering a network device may be one of a unicastpacket, a broadcast packet, a muliticast packet, or an unknown unicastpacket. The unicast packet is transmitted to a specific destinationaddress that can be determined by the receiving network device. However,the sending network device must select one port from the trunk group andadequately distribute packets across ports of the trunk group.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention thattogether with the description serve to explain the principles of theinvention, wherein:

FIG. 1 illustrates a network device in which an embodiment of thepresent invention may be implemented;

FIG. 2 illustrates a centralized ingress pipeline architecture,according to one embodiment of the present invention;

FIG. 3 illustrates an embodiment of the network in which multiplenetwork devices are connected by trunks; and

FIG. 4 illustrates a trunk group table that is used in an embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference will now be made to the preferred embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings.

FIG. 1 illustrates a network device, such as a switching chip, in whichan embodiment the present invention may be implemented. Device 100includes an ingress module 102, a MMU 104, and an egress module 106.Ingress module 102 is used for performing switching functionality on anincoming packet. MMU 104 is used for storing packets and performingresource checks on each packet. Egress module 106 is used for performingpacket modification and transmitting the packet to an appropriatedestination port. Each of ingress module 102, MMU 104 and Egress module106 includes multiple cycles for processing instructions generated bythat module. Device 100 implements a pipelined approach to processincoming packets. The device 100 has the ability of the pipeline toprocess, according to one embodiment, one packet every clock cycle.According to one embodiment of the invention, the device 100 includes a133.33 MHz core clock. This means that the device 100 architecture iscapable of processing 133.33M packets/sec.

Device 100 may also include one or more internal fabric high speedports, for example a HiGig™, high speed port 108 a-108 x, one or moreexternal Ethernet ports 109 a-109 x, and a CPU port 110. High speedports 108 a-108 x are used to interconnect various network devices in asystem and thus form an internal switching fabric for transportingpackets between external source ports and one or more externaldestination ports. As such, high speed ports 108 a-108 x are notexternally visible outside of a system that includes multipleinterconnected network devices. CPU port 110 is used to send and receivepackets to and from external switching/routing control entities or CPUs.According to an embodiment of the invention, CPU port 110 may beconsidered as one of external Ethernet ports 109 a-109 x. Device 100interfaces with external/off-chip CPUs through a CPU processing module111, such as a CMIC, which interfaces with a PCI bus that connectsdevice 100 to an external CPU.

Network traffic enters and exits device 100 through external Ethernetports 109 a-109 x. Specifically, traffic in device 100 is routed from anexternal Ethernet source port to one or more unique destination Ethernetports 109 a-109 x. In one embodiment of the invention, device 100supports physical Ethernet ports and logical (trunk) ports. A physicalEthernet port is a physical port on device 100 that is globallyidentified by a global port identifier. In an embodiment, the globalport identifier includes a module identifier and a local port numberthat uniquely identifies device 100 and a specific physical port. Thetrunk ports are a set of physical external Ethernet ports that act as asingle link layer port. Each trunk port is assigned a global a trunkgroup identifier (TGID). According to an embodiment, device 100 cansupport up to 128 trunk ports, with up to 8 members per trunk port, andup to 29 external physical ports. Destination ports 109 a-109 x ondevice 100 may be physical external Ethernet ports or trunk ports. If adestination port is a trunk port, device 100 dynamically selects aphysical external Ethernet port in the trunk by using a hash to select amember port. As explained in more detail below, the dynamic selectionenables device 100 to allow for dynamic load sharing between ports in atrunk.

Once a packet enters device 100 on a source port 109 a-109 x, the packetis transmitted to ingress module 102 for processing. Packets may enterdevice 100 from a XBOD or a GBOD. The XBOD is a block that has one10GE/12G MAC and supports packets from high speed ports 108 a-108 x. TheGBOD is a block that has 12 10/100/1G MAC and supports packets fromports 109 a-109 x.

FIG. 2 illustrates a centralized ingress pipeline architecture 200 ofingress module 102. Ingress pipeline 200 processes incoming packets,primarily determines an egress bitmap and, in some cases, figures outwhich parts of the packet may be modified. Ingress pipeline 200 includesa data holding register 202, a module header holding register 204, anarbiter 206, a configuration stage 208, a parser stage 210, a discardstage 212 and a switch stage 213. Ingress pipeline 200 receives datafrom the XBOD, GBOD or CPU processing module 111 and stores cell data indata holding register 202. Arbiter 206 is responsible for schedulingrequests from the GBOD, the XBOD and CPU. Configuration stage 208 isused for setting up a table with all major port-specific fields that arerequired for switching. Parser stage 210 parses the incoming packet anda high speed module header, if present, handles tunnelled packetsthrough Layer 3 (L3) tunnel table lookups, generates user definedfields, verifies Internet Protocol version 4 (IPv4) checksum on outerIPv4 header, performs address checks and prepares relevant fields fordownstream lookup processing. Discard stage 212 looks for various earlydiscard conditions and either drops the packet and/or prevents it frombeing sent through pipeline 200. Switching stage 213 performs all switchprocessing in ingress pipeline 200, including address resolution.

According to one embodiment of the invention, the ingress pipelineincludes one 1024-bit cell data holding register 202 and one 96-bitmodule header register 204 for each XBOD or GBOD. Data holding register202 accumulates the incoming data into one contiguous 128-byte cellprior to arbitration and the module header register 204 stores anincoming 96-bit module header for use later in ingress pipeline 200.Specifically, holding register 202 stores incoming status information.

Ingress pipeline 200 schedules requests from the XBOD and GBOD every sixclock cycles and sends a signal to each XBOD and GBOD to indicate whenthe requests from the XBOD and GBOD will be scheduled. CPU processingmodule 111 transfers one cell at a time to ingress module 102 and waitsfor an indication that ingress module 102 has used the cell beforesending subsequent cells. Ingress pipeline 200 multiplexes signals fromeach of XBOD, GBOD and CPU processing based on which source is grantedaccess to ingress pipeline 200 by arbiter 206. Upon receiving signalsfrom the XBOD or GBOD, a source port is calculated by register buffer202, the XBOD or GBOD connection is mapped to a particular physical portnumber on device 100 and register 202 passes information relating to ascheduled cell to arbiter 206.

When arbiter 206 receives information from register buffer 202, arbiter206 may issue at least one of a packet operation code, an instructionoperation code or a FP refresh code, depending on resource conflicts.According to one embodiment, the arbiter 206 includes a main arbiter 207and auxiliary arbiter 209. The main arbiter 207 is a time-divisionmultiplex (TDM) based arbiter that is responsible for schedulingrequests from the GBOD and the XBOD, wherein requests from main arbiter207 are given the highest priority. The auxiliary arbiter 209 schedulesall non XBOD/GBOD requests, including CPU packet access requests, CPUmemory/register read/write requests, learn operations, age operations,CPU table insert/delete requests, refresh requests and rate-limitcounter refresh request. Auxiliary arbiter's 209 requests are scheduledbased on available slots from main arbiter 207.

When the main arbiter 207 grants an XBOD or GBOD a slot, the cell datais pulled out of register 202 and sent, along with other informationfrom register 202, down ingress pipeline 200. After scheduling theXBOD/GBOD cell, main arbiter 207 forwards certain status bits toauxiliary arbiter 209.

The auxiliary arbiter 209 is also responsible for performing allresource checks, in a specific cycle, to ensure that any operations thatare issued simultaneously do not access the same resources. As such,auxiliary arbiter 209 is capable of scheduling a maximum of oneinstruction operation code or packet operation code per request cycle.According to one embodiment, auxiliary arbiter 209 implements resourcecheck processing and a strict priority arbitration scheme. The resourcecheck processing looks at all possible pending requests to determinewhich requests can be sent based on the resources that they use. Thestrict priority arbitration scheme implemented in an embodiment of theinvention requires that CPU access request are given the highestpriority, CPU packet transfer requests are given the second highestpriority, rate refresh request are given the third highest priority, CPUmemory reset operations are given the fourth highest priority and Learnand age operations are given the fifth highest priority by auxiliaryarbiter 209. Upon processing the cell data, auxiliary arbiter 209transmits packet signals to configuration stage 208.

Configuration stage 208 includes a port table for holding all major portspecific fields that are required for switching, wherein one entry isassociated with each port. The configuration stage 208 also includesseveral registers. When the configuration stage 208 obtains informationfrom arbiter 206, the configuration stage 208 sets up the inputs for theport table during a first cycle and multiplexes outputs for other portspecific registers during a second cycle. At the end of the secondcycle, configuration stage 208 sends output to parser stage 210.

Parser stage 210 manages an ingress pipeline buffer which holds the128-byte cell as lookup requests traverse pipeline 200. When the lookuprequest reaches the end of pipeline 200, the data is pulled from theingress pipeline buffer and sent to MMU 104. If the packet is receivedon a high speed port, a 96-bit module header accompanying the packet isparsed by parser stage 210. After all fields have been parsed, parserstage 210 writes the incoming cell data to the ingress pipeline bufferand passes a write pointer down the pipeline. Since the packet data iswritten to the ingress pipeline buffer, the packet data need not betransmitted further and the parsed module header information may bedropped. Discard stage 212 then looks for various early discardconditions and, if one or more of these conditions are present, discardstage drops the packet and/or prevents it from being sent through thechip.

Switching stage 213 performs address resolution processing and otherswitching on incoming packets. According to an embodiment of theinvention, switching stage 213 includes a first switch stage 214 and asecond switch stage 216. First switch stage 214 resolves any dropconditions, performs BPDU processing, checks for layer 2 source stationmovement and resolves most of the destination processing for layer 2 andlayer 3 unicast packets, layer 3 multicast packets and IP multicastpackets. The first switch stage 214 also performs protocol packetcontrol switching by optionally copying different types of protocolpackets to the CPU or dropping them. The first switch stage 214 furtherperforms all source address checks and determines if the layer 2 entryneeds to get learned or re-learned for station movement cases. The firstswitch stage 214 further performs destination calls to determine how toswitch packet based on a destination switching information.Specifically, the first switch stage 214 figures out the destinationport for unicast packets or port bitmap of multicast packets, calculatesa new priority, optionally traps packets to the CPU and drops packetsfor various error conditions. The first switch stage 214 further handleshigh speed switch processing separate from switch processing from port109 a-109 i and switches the incoming high speed packet based on thestage header operation code.

The second switch stage 216 then performs Field Processor (FP) actionresolution, source port removal, trunk resolution, high speed trunking,port blocking, CPU priority processing, end-to-end Head of Line (HOL)resource check, resource check, mirroring and maximum transfer length(MTU) checks for verifying that the size of incoming/outgoing packets isbelow a maximum transfer length. The second switch stage 216 takes firstswitch stage 216 switching decision, any layer routing information andFP redirection to produce a final destination for switching. The secondswitch stage 216 also removes the source port from the destination portbitmap and performs trunk resolution processing for resolving thetrunking for the destination port for unicast packets, the ingressmirror-to-port and the egress mirror-to-port. The second switch stage216 also performs high speed trunking by checking if the source port ispart of a high speed trunk group and, if it is, removing all ports ofthe source high speed trunk group. The second switch stage 216 furtherperforms port blocking by performing masking for a variety of reasons,including meshing and egress masking.

FIG. 3 illustrates an embodiment of a network in which multiple networkdevices, as described above, are connected by trunks. According to FIG.3, network 300 includes devices 302-308 which are connected by trunks310-316. Device 302 includes ports 1 and 2 in trunk group 310, device304 includes ports 4 and 6 in trunk group 310 and device 306 includesports 10 and 11 in trunk group 310. Each of network devices 302-308 mayreceive unicast or multicast packets that must be transmitted to anappropriate destination port. As is known to those skilled in the art,in the case of unicast packets, the destination port is a known port. Tosend a unicast packet to an appropriate port in a destination trunk,each of network devices 302-308 includes a trunk group table 400,illustrated in FIG. 4.

As noted above, an embodiment of device 100 may support up to 128 trunkports with up to 8 members per trunk port. As such, table 400 is a 128entry table, wherein each entry includes fields for eight ports.Therefore, returning to FIG. 3, for trunk group 310, an associated entryin table 400 is entry 0 which includes a field for each module and portin that trunk group. As such, entry 0 of table 400 includes in field402, module ID 302 and port ID 1, in field 404, module ID 302 and portID 2, in field 406, module ID 304 and port ID 4, in field 408, module ID304 and port ID 6, in field 410, module ID 306 and port ID 10 and infield 412, module ID 306 and port ID 11. Since trunk group 310 only hassix ports, the last two fields 414 and 416 in entry 0 may includeredundant information from any of fields 402-412 of that entry. Table400 also includes an R-TAG value in each entry. In an embodiment of theinvention, the RTAG value may be one of six options, wherein each optionis used to identify predefined fields and certain bits are selected fromeach field. Thereafter, all of the values from each of the predefinedfields are XORed to obtain a number between 0 and 7, wherein a portassociated with the obtained number is selected from the trunk group totransmit the packet to a destination device. Different RTAGs are used toobtain different types of distribution. Since the distribution isdependent on the packet, the RTAG enables the device to spread packetdistribution over all the ports in a given trunk group. In oneembodiment of the invention, if the RTAG value is set to 1, the port isselected based on the source address (SA), the VLAN, the EtherType, thesource module ID (SRC_MODID) and the source port (SRC_PORT) of thepacket. If the RTAG value is set to 2, the port is selected based on thedestination address (DA), the VLAN, the EtherType, the source module IDand the source port of the packet. If the RTAG value is set to 3, theport is selected based on the source address, the destination address,the VLAN, the EtherType, the source module ID and the source port of thepacket. RTAGs 4, 5 and 6 provide a layer 3 header option. If the RTAGvalue is set to 4, the port is selected based on the source IP address(SIP) and the TCP source port (TCP_SPORT). If the RTAG value is set to5, the port is selected based on the destination IP address (DIP) andthe TCP destination port (TDP_DPORT). If the RTAG value is set to 6, theport is selected based on a value obtained from XORing an RTAG 4 hashand an RTAG 5 hash.

Specifically, in one embodiment of the invention, since each entry oftrunk group table includes eight fields that are associated with trunkgroup ports, three bits are selected from each byte of the fields in theRTAG hash to represent 8 bits. So if the RTAG value is 1, SA[0:2],SA[8:10], SA[16:18], SA[32:34] and SA[40:42], VLAN[0:2], VLAN [8:10],EtherType[0:2], EtherType[8:10], SRC_MODID[0:2] and SRC_PORT[0:2] areXORed to obtain a three bit value that is used to index trunk grouptable 400. If the RTAG value is 2, DA[0:2], DA[8:10], DA[16:18],DA[32:34], SA[40:42], VLAN[0:2], VLAN [8:10], EtherType[0:2],EtherType[8:10], SRC_MODID[0:2] and SRC_PORT[0:2] are XORed to obtain athree bit value that is used to index trunk group table 400. If the RTAGvalue is 3, SA[0:2], SA[8:10], SA[16:18], SA[32:34], SA[40:42], DA[0:2],DA[8:10], DA[16:18], DA[32:34], DA[40:42], VLAN[0:2], VLAN [8:10],EtherType[0:2], EtherType[8:10], SRC_MODID[0:2] and SRC_PORT[0:2] areXORed to obtain a three bit value that is used to index trunk grouptable 400.

If the RTAG value is 4, SIP[0:2], SIP[8:10], SIP[16:18], SIP[32:34],SIP[40:42], SIP[48:50], SIP[56:58], SIP[66:64], SIP[72:74], SIP[80:82],SIP[88:90], SIP[96:98], SIP[104:106], SIP[112:114], SIP[120:122],TCP_SPORT[0:2] and TCP_SPORT[8:10] are XORed to obtain a three bit valuethat is used to index trunk group table 400. If the RTAG value is 5,DIP[0:2], DIP[8:10], DIP[16:18], DIP[32:34], DIP[40:42], DIP[48:50],DIP[56:58], DIP[66:64], DIP[72:74], DIP[80:82], DIP[88:90], DIP[96:98],DIP[104:106], DIP[112:114], DIP[120:122], TCP_DPORT[0:2] andTCP_SPORT[8:10] are XORed to obtain a three bit value that is used toindex trunk group table 400.

For example, in FIG. 3, upon receiving a unicast packet by networkdevice 308 for further transmission on trunk group 310, ingress module102 in device 308 performs a destination lookup which points to trunkgroup 310. Network device then indexes an appropriate entry, i.e. entry0, in trunk group table 400. To determine which port to select fromtrunk group 310, device 308 implements a trunk hashing algorithm basedon the RTAG value in entry 0. Since the RTAG value in entry 0 is 1,device 308 obtains a three bit index that is used to access one field ofentry 0 by XORing SA[0:2], SA[8:10], SA[16:18], SA[32:34] and SA[40:42],VLAN[0:2], VLAN [8:10], EtherType[0:2], EtherType[8:10], SRC_MODID[0:2]and SRC_PORT[0:2]. Upon accessing, for example, the third field, thepacket is sent to port 4 of device 304.

The above-discussed configuration of the invention is, in a preferredembodiment, embodied on a semiconductor substrate, such as silicon, withappropriate semiconductor manufacturing techniques and based upon acircuit layout which would, based upon the embodiments discussed above,be apparent to those skilled in the art. A person of skill in the artwith respect to semiconductor design and manufacturing would be able toimplement the various modules, interfaces, and tables, buffers, etc. ofthe present invention onto a single semiconductor substrate, based uponthe architectural description discussed above. It would also be withinthe scope of the invention to implement the disclosed elements of theinvention in discrete electronic components, thereby taking advantage ofthe functional aspects of the invention without maximizing theadvantages through the use of a single semiconductor substrate.

With respect to the present invention, network devices may be any devicethat utilizes network data, and can include switches, routers, bridges,gateways or servers. In addition, while the above discussionspecifically mentions the handling of packets, packets, in the contextof the instant application, can include any sort of datagrams, datapackets and cells, or any type of data exchanged between networkdevices.

The foregoing description has been directed to specific embodiments ofthis invention. It will be apparent, however, that other variations andmodifications may be made to the described embodiments, with theattainment of some or all of their advantages. Therefore, it is theobject of the appended claims to cover all such variations andmodifications as come within the true spirit and scope of the invention.

1. A network device for selecting a port from a trunk group to transmita unicast packet on the selected port, the network device comprising: atleast one trunk group comprising a plurality of physical ports; a tablecomprising a plurality of entries, wherein each entry is associated withone trunk group and comprises a plurality of fields that are associatedwith ports in the trunk group and wherein each entry comprises a hashfield that is used to select bits from predefined fields of an incomingunicast packet to obtain an index bit for accessing one of the pluralityof fields; and transmitting means for transmitting the unicast packet toa port associated with an accessed field of the plurality of fields. 2.The network device according to claim 1, wherein the table is configuredas a 128 entry table, wherein each entry comprises fields for eightports.
 3. The network device according to claim 1, wherein each of theplurality of fields are configured to include an identifier for thenetwork device and an identifier for one of the plurality of physicalports in the trunk group.
 4. The network device according to claim 1,wherein if the trunk group comprises less than eight ports, the table isconfigured store redundant information from at least one of theplurality of fields in at least another one of the plurality of fields.5. The network device according to claim 1, wherein the network isconfigured to store one of a plurality of values in the hash field,wherein each of the plurality of values identifies predefined fields inthe unicast packet.
 6. The network device according to claim 5, furthercomprising hashing means for hashing predefined bits from the identifiedpredefined fields to obtain the index bit for accessing one of theplurality of fields.
 7. The network device according to claim 5, whereinthe network device is configured to obtain different distribution types,according to the plurality of values, for distributing incoming packetsto ports of the trunk group.
 8. The network device according to claim 5,wherein the network device is configured to hash, if a value of the hashfield is one, predefined bits from a source address, a VLAN, anEthertype, a source module identifier and a source port associated withthe unicast packet to obtain the index bit for accessing one of theplurality of fields.
 9. The network device according to claim 5, whereinthe network device is configured to hash, if a value of the hash fieldis two, predefined bits from a destination address, a VLAN, anEthertype, a source module identifier and a source port associated withthe unicast packet to obtain the index bit for accessing one of theplurality of fields.
 10. The network device according to claim 5,wherein the network device is configured to hash, if a value of the hashfield is three, predefined bits from a source address, a destinationaddress, a VLAN, an Ethertype, a source module identifier and a sourceport associated with the unicast packet to obtain the index bit foraccessing one of the plurality of fields.
 11. The network deviceaccording to claim 5, wherein the network device is configured to hash,if a value of the hash field is four, predefined bits from a source IPaddress, and a TCP source port associated with the unicast packet toobtain the index bit for accessing one of the plurality of fields. 12.The network device according to claim 5, wherein the network device isconfigured to hash, if a value of the hash field is five, predefinedbits from a destination IP address, and a TCP destination portassociated with the unicast packet to obtain the index bit for accessingone of the plurality of fields.
 13. The network device according toclaim 5, wherein the network device is configured to hash, if a value ofthe hash field is six, predefined bits from a source IP address, a TCPsource port, a destination IP address and a TCP destination portassociated with the unicast packet to obtain the index bit for accessingone of the plurality of fields.
 14. A method for selecting a port from atrunk group to transmit a unicast packet on the selected port, themethod comprising the steps of: associating each entry of a table with atrunk group comprising a plurality of physical ports; storing in each ofa plurality of fields of each entry, information associated with one ofthe plurality of ports in the trunk group; storing, in each entry of thetable, a hash field that is used to select bits from predefined fieldsof an incoming unicast packet; thereafter, receiving the incomingunicast packet for further transmission on one of the plurality of portof the trunk; obtaining an index bit through the hash field foraccessing one of the plurality of fields in the entry; and transmittingthe unicast packet to a port associated with an accessed one of theplurality of fields.
 15. The method according to claim 14, furthercomprising the step of storing, if the trunk group comprises less thaneight ports, redundant information from at least one of the plurality offields in at least another one of the plurality of fields.
 16. Themethod according to claim 14, further comprising hashing predefined bitsfrom predefined fields of the incoming unicast packet to obtain theindex bit for accessing one of the plurality of fields.
 17. The methodaccording to claim 14, further comprising hashing, if a value of thehash field is one, predefined bits from a source address, a VLAN, anEthertype, a source module identifier and a source port associated withthe unicast packet to obtain the index bit for accessing one of theplurality of fields.
 18. The method according to claim 14, furthercomprising hashing, if a value of the hash field is two, predefined bitsfrom a destination address, a VLAN, an Ethertype, a source moduleidentifier and a source port associated with the unicast packet toobtain the index bit for accessing one of the plurality of fields. 19.The method according to claim 14, further comprising hashing, if a valueof the hash field is three, predefined bits from a source address, adestination address, a VLAN, an Ethertype, a source module identifierand a source port associated with the unicast packet to obtain the indexbit for accessing one of the plurality of fields.
 20. The methodaccording to claim 14, further comprising hashing, if a value of thehash field is four, predefined bits from a source IP address, and a TCPsource port associated with the unicast packet to obtain the index bitfor accessing one of the plurality of fields.
 21. The method accordingto claim 14, further comprising hashing, if a value of the hash field isfive, predefined bits from a destination IP address, and a TCPdestination port associated with the unicast packet to obtain the indexbit for accessing one of the plurality of fields.
 22. The methodaccording to claim 14, further comprising hashing, if a value of thehash field is six, predefined bits from a source IP address, a TCPsource port, a destination IP address and a TCP destination portassociated with the unicast packet to obtain the index bit for accessingone of the plurality of fields.
 23. An apparatus for selecting a portfrom a trunk group to transmit a unicast packet on the selected port,the apparatus comprising: associating means for associating each entryof a table with a trunk group comprising a plurality of physical ports;storing means for storing in each of a plurality of fields of eachentry, information associated with one of the plurality of ports in thetrunk group; storing means for storing, in each entry of the table, ahash field that is used to select bits from predefined fields of anincoming unicast packet; receiving means for receiving the incomingunicast packet for further transmission on one of the plurality of portof the trunk; obtaining means for obtaining an index bit through thehash field for accessing one of the plurality of fields in the entry;and transmitting means for transmitting the unicast packet to the portassociated with an accessed one of the plurality of fields.